Immune complex size and complement regulate cytokine production by peripheral blood mononuclear cells.

Area of Science:

• Immunology
• Rheumatology
• Cellular Biology

Background:

• Immune complexes in juvenile rheumatoid arthritis (JRA) exhibit variable size, composition, and inflammatory potential.
• Understanding the factors governing immune complex proinflammatory effects is crucial for JRA pathogenesis.

Purpose of the Study:

• To elucidate the specific roles of size and composition in immune complex-mediated inflammation.
• To investigate how complement influences the inflammatory capacity of immune complexes.

Main Methods:

• Incubation of peripheral blood mononuclear cells (PBMCs) with distinct immune complex preparations (opsonized, unopsonized, complement-solubilized).
• Enzyme-linked immunosorbent assay (ELISA) to quantify IL-1beta and IL-8 secretion.
• Sucrose density gradient ultracentrifugation to assess immune complex size.
• Complement component C4 binding assays.

Main Results:

• Immune complexes formed with complement were less potent inducers of IL-1beta and IL-8 than unopsonized complexes.
• Complement-solubilized immune precipitates demonstrated intermediate cytokine induction capacity.
• Unopsonized complexes and solubilized precipitates were larger than opsonized complexes.
• Fluid-phase C4 binding, without altering size, enhanced IL-1beta secretion.

Conclusions:

• Complement significantly modulates the inflammatory response to immune complexes, partly through size regulation.
• Immune complex size is a critical determinant of their capacity to stimulate leukocyte cytokine secretion.
• Further research into complement's role in JRA immune complexes is warranted.